Given an integer , return if it is a power of four. Otherwise, return . n true false An integer is a power of four, if there exists an integer such that . n x n == 4x Example 1: Input: n = 16
Output: true Example 2: Input: n = 5
Output: false Example 3: Input: n = 1
Output: true Solution: The easiest way how to solve this problem is to  divide N on 4 and that is it. We will iterate again and again till our number is bigger than 1. public boolean isPowerOfFour(int n) {
    if (n == 0){
        return false;
    }
    
    while(n != 1){
        if (n % 4 != 0){
            return false;
        }
        n /= 4;
    }
    return true;
} But also we can use recursion: public boolean isPowerOfFour(int n) {
        return check(n, 1);
    }

    boolean check(int n, long value) {
        if (value >= n) return n == value;

        return check(n, value * 4);
    } And sure, we can solve it with math, but I don’t want to share it with you. Because for me, you usually cannot find a mathematical solution without solving this problem before. Does it clear? Write your comments. ok ok and out next problem for today Reverse Vowels of a String Given a string , reverse only all the vowels in the string and return it. s The vowels are , , , , and , and they can appear in both cases. 'a' 'e' 'i' 'o' 'u' Example 1: Input: s = "hello"
Output: "holle" Example 2: Input: s = "leetcode"
Output: "leotcede" Solution: To solve this problem, we will use the popular technique of two-pointers. The main idea of solving problems like this -- is to understand base techniques and use them later in medium and hard problems. We are going to prepare a vowel dictionary. Then we can iterate in both directions. If both pointers stay on the vowels we can swap them. And continue our direction. public String reverseVowels(String s) {
    Set<Character> dict = new HashSet<>();
    dict.add('a');
    dict.add('A');
    dict.add('e');
    dict.add('E');
    dict.add('i');
    dict.add('I');
    dict.add('o');
    dict.add('O');
    dict.add('u');
    dict.add('U');

    int reader = 0;
    int writer = s.length() - 1;

    StringBuilder sb = new StringBuilder(s);
    while (reader < writer) {
        if(!dict.contains(s.charAt(reader))){
            reader ++;
        }
        if (!dict.contains(s.charAt(writer))){
            writer--;
        }
        if (dict.contains(s.charAt(reader)) && dict.contains(s.charAt(writer))){
            char tmp = s.charAt(reader);
            sb.setCharAt(reader++, s.charAt(writer));
            sb.setCharAt(writer--, tmp);
        }
    }
    return sb.toString();
} Does it clear? Write your comments.

The code in this story is for educational purposes. The readers are solely responsible for whatever they build with it.

Finding Product of Array Except Self

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Power of Four and Reverse Vowels of a String

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